1. Field of the Invention
The present invention relates generally to superconducting cable joint structures and more specifically to effectively preventing a conductor connection from overheating in jointing and thus connecting an end of a core of a superconducting cable to a counterpart conductor.
2. Description of the Background Art
Currently, cities and the like have a tendency to consume increasing amounts of power, and accordingly require larger underground power transmission capacities. Accordingly, a superconducting cable allowing as large a current density as approximately 100 times that of a conventional cable is being developed. This superconducting cable is, as disclosed for example in Japanese Patent Laying-Open No. 2002-140943, structured such that a plurality of cable cores having a superconductor pass through an external casing's internal space having liquid nitrogen or the like flowing therethrough to serve as a coolant layer.
To lay the aforementioned superconducting cable underground, it is necessary to connect together such superconducting cables of a prescribed length. Currently, however, there has not been a method proposed to suitably joint a superconducting cable currently being studied. Japanese Patent Laying-Open No. 7-335358 discloses jointing and thus connecting together a conventional, non-superconducting power cable and a counterpart power cable. More specifically, as shown in FIG. 11, power cables 1 have their respective ends with their respective, exposed conductors 2 abutting against each other and connected together by a conductor connection sleeve 3 externally fitted thereon and furthermore they are externally, circumferentially surrounded by an oil impregnated paper.
However, if the method of jointing conventional power cables 1 together, as shown in FIG. 11, is employed to joint and thus connect together cores of superconducting cables, respectively, conductor connection sleeve 3, which is a normal conductor, and a superconductor will be connected together. This provides an increased value in resistance at a portion connecting the normal conductor and the superconductor together. As a result, an increased quantity of heat is generated and a coolant surrounding the cable cores may bubble and as a result destroy a coolant impregnated paper, and to maintain the cable's superconducting property a refrigerator having a large capacity is required. Furthermore, the increased resistance at the portion connecting the conductor connection sleeve of the normal conductor and the superconductor together, contributes to a reduced current capacity of the superconducting cable in its entirety.